1. Field of the Invention
The present invention relates to a blood pump, such as total or assistant artificial heart to be implanted.
2. Description of the Prior Art
One known total artificial heart to be implanted is the so-called pusher-plate type in which inflow and outflow of blood into or from a blood chamber are accomplished through the intermediation of a reciprocating pusher-plate.
The pusher plate is driven, for example, by a reversible DC brushless motor through a cam mechanism by which rotation of the motor is converted into reciprocating movement [Trans. Am. Soc. Artif Intern Organs Vol, XXX, pp 69-74 (1984)]. The possible application of a Stirling engine or shape memory alloy for the same purpose is under study.
A DC motor is particularly attractive such a drive means. It however is disadvantageous in that it is impossible to produce larger output without, for example, enhancing coil capacity, resulting in increasing its weight. That is, higher energy conversion efficiency is contrary to realization of a lighter and smaller-sized device, thus simultaneous fulfillment of both being impossible. Another defect is that a DC motor generates electromagnetic waves which may affect a Hall effect sensor disposed near it used for sensing movement information of the pusher-plate (or blood flow) and may cause the drive-control system to undergo noise problems, possibly resulting in erroneous operation. Further conductivity of the motor shaft and coils renders it difficult to completely insulate the motor from the housing of the artificial heart, and in turn to secure the electrical safety of it as a medical electric device.